The Jones Creek trail is specifically maintained for off road vehicle use, motorcycles and ATVs. If you use the trail for hiking or mountain biking, you need to remain alert for the approach of off road vehicles and allow them passage. The main trail is closed to off road vehicles from December 1st to May 1st, so that would be a time it could be hiked without concern, except that the trail would likely also be muddy in places or have snow during the winter months.
I hiked the trail early in May. I came across a couple muddy spots, but nothing that prevented me from getting through. I started my hike very early on a weekday morning and was able to hike for a couple hours before any motorcycles showed up. I remained alert, and just had three times on the 11 mile hike that I had to step aside to let dirt bikes pass. Overall it was an enjoyable hike. If you have a bike or ATV that you want to take out for a great ride, this would definitely be the place to go.
The Jones Creek Trail makes about an 11 mile loop. It connects to other trails and roads in the area that can add many more miles. The Jones Creek Trail Riders Association maintains it, and has a website with useful details and updates.
Bridge on Jones Creek Trail 
The parking lot is in the distance 
A stream crossing on Jones Creek Trail 
Jones Creek Trail 
Mt. Hood seen from Jones Creek Trail 
Jones Creek Trail 
Baz Trail junction with Jones Creek Trail 
Jones Creek Trail winds through a clear cut 
Jones Creek Trail
Was wondering how much single track has been biult?
Sorry, I don’t know the answer to that question. There are definitely more than a couple miles of trails that you could ride. I should add that if you are looking for a good place to ride, this is definitely worth checking out. There are one-way trails to avoid conflict, and when you add the gravel roads there are many miles to explore.
For more details I suggest you check out https://jctra.org/ and contact the Jones Creek Riders Association.